Structure reactivity relationships during N2O hydrogenation over Au-Ag alloys: A study by field emission techniques

Abstract To make available atomic oxygen at the surface of a catalyst is the key step for oxidation reactions on Au-based catalysts. In this context, Au-Ag alloys catalysts exhibit promising properties for selective oxidation reactions of alcohols: low temperature activity and high selectivity. The presence of O(ads) and its effects on the catalytic reactivity is studied via the N 2 O dissociative adsorption and subsequent hydrogenation. Field emission techniques are particularly suited to study this reaction: Field Ion Microscopy (FIM) and Field Emission Microscopy (FEM) enable to image the extremity of sharp metallic tips, the size and morphology of which are close to those of one single catalytic particle. The reaction dynamics is studied in the 300–320 K temperature range and at a pressure of 3.5  ×  10 −3 Pa. The main results are a strong structure/reactivity relationship during N 2 O + H 2 reaction over Au-8.8 at.%Ag model catalysts. Comparison of high-resolution FIM images of the clean sample and FEM images during reaction shows a sensitivity of the reaction to the local structure of the facets, independently of the used partial pressures of both N 2 O and H 2 . This suggests a localised dissociative adsorption step for N 2 O and H 2 with the formation of a reactive interface around the {210} facets.